The invention relates to a data processing system based on a 100% redundancy four-symbol code-word code having both single-symbol error correctability and plural error mendability with respect to at least two symbols in one code word coexistently, said system having:
a. a decoder stage having an input for receiving code words and to therefrom deriving two-symbol data words; PA1 b. a processor stage fed by said decoder stage to process said data words for therefrom developing memory addresses and further data words; PA1 c. an encoding stage having multiple encoder modules for receiving intendedly identical versions of a selection of said data words and for in respective encoder modules encoding unto respective different code symbols: PA1 d. a memory stage having multiple memory modules each fed by a respective one of said encoder modules for under control of said memory addresses collectively writing and reading all code symbols of an associated code word; PA1 e. feedback means fed by said memory modules for retrocoupling any code word so read to said decoder stage. U.S. Pat. No. 4,512,020 (PHN 10155, code 81), especially FIG. 24 thereof describes a four-module system that allows one module to completely fail without rendering the overall system inoperative. Symbols of a code word have a uniform length of a plurality of bits, in the reference of four bits. Correctible means that an arbitrary disturbance can be determined quantitatively and thereupon restored. So, both the questions as "where" the disturbance occurs and "what" the disturbance is, are answered. On the level of a single bit these two notions are identical. On the level of a plural-bit symbol, pointing the disturbed symbol is only the first step in realizing the correction. On the other hand, mendable is understood to mean that the effect of an error can be made inconsequential. In addition to full correction, this includes the possibility for declaring one or more particular symbols invalid or "erased" so that they would have no bearing for retrieving the code word's data content. Of course, such erasure renders the remainder of the code word less robust against further disturbances. On a higher level, mendability may on the level of the code proper also be restricted to detecting-only of the error. Then, the measures effectively taken could be a retry of the operation that would make a soft error presumedly invisible, a recourse to a higher-level authority such as a background memory, or just the being on one's guard as to the incorrectness encountered. PA1 a. a decoder stage having an input for receiving code words and to therefrom deriving k-symbol data words; b. a processor stage fed by said decoder stage to process any word received for therefrom developing memory addresses and further data words; PA1 c. an encoding stage having multiple encoder modules for receiving intendedly identical versions of each of a selection of said further data words for in respective encoder modules encoding unto respective different code symbols of the associated code word; PA1 d. a memory stage having multiple memory modules each fed by a respective one of said encoder modules for under control of an associated one of said memory addresses collectively writing and reading all code words of said associated code word; PA1 e. feedback means fed by said memory modules for retrocoupling any code word so read to said decoder stage,